There may be no vacancy yet for the job. But the jockeying for position in the race to become the next director general of the BBC has already begun – even though Mark Thompson has signalled no desire to quit.

The search for a new director of BBC Vision – a key role overseeing the corporation's TV channels and production departments – has encouraged a number of executives to quietly start campaigning to become the corporation's 15th DG. It has also alerted the BBC Trust, which appoints the director general, and is considering who might succeed Thompson whenever the time comes. The headhunters in charge of the Vision appointment, insiders say, have been tasked with two objectives – to find someone who can follow in Jana Bennett's footsteps and be a credible internal future candidate for director general.

However, all this may seem somewhat premature, as it all depends on when Thompson decides to leave. Friends of Thompson find it distasteful that would-be successors are manoeuvring already as he battles to make the cuts required by the six-year licence fee freeze. They say he is irritated by the distracting speculation that he may step down after the Olympics next year. Already the BBC has denied reports that top US talent agency CAA has unofficially been looking to act for him.

Such is the delicate nature of the succession issue that few people want to comment on the record about who they think might follow in his footsteps. The BBC declines to comment. One BBC source compared it with a papal succession, where candidates do not compete openly, perhaps apposite for the Catholic Thompson.

Political jousting

His reign began in May 2004 after his predecessor Greg Dyke left following the Hutton report. Thompson has survived and cleared up after what outgoing BBC Trust chairman Sir Michael Lyons called some "memorable cock-ups". These included the Crowngate affair, which led to the departure of the BBC1 controller Peter Fincham, the Jonathan Ross and Russell Brand scandal, and viewer deceptions such as the renaming of the Blue Peter cat. The fallout has been more stringent editorial guidelines, more compliance and more public scrutiny.

Against a background of political jousting – which led to a six-year licence fee deal – continuing efficiency savings and moving 2,300 jobs to the BBC's new northern headquarters in Salford, Thompson has not had an easy time.

So, despite the big pay packet (£600,000 a year) and kudos, there are big drawbacks. Who is tough and savvy enough to take on a job like this?

Someone who knows is ex-DG Greg Dyke. He explains: "You need some sort of hard skin, you have to not get too upset when people make nasty attacks on you and the organisation. You have to inspire a lot of people. What the BBC needs and what the next director general needs to do is to pull the people who like and respect the BBC together, which has been lost a bit.

"Mark has been a good director general in a very difficult time. He's had a harder time than I did, other than with Hutton obviously. He's gone through an economic hard time. I was lucky I lived through the good financial years."

The former boss reckons that after the Olympics and the BBC's move to Salford next year is "likely to be a perfect time for Mark to leave – on a high".

However, whether he will do so depends, of course, on the BBC's political and financial climate at the time. Nobody can foresee whether an issue may blow up – like Ross/Brand – and ruin Thompson's private retirement plans.

But if the climate remains benign, such is the strength of Thompson's position that he could yet outlast previous long-serving director generals, Hugh Carleton Greene (nine years) and John Reith (11 years).

Neverthless, even though Thompson is still firmly in his post, a number of heads are popping up above the parapet.

Undoubtedly the Vision role is one of the biggest in television – overseeing more than 20,000 hours of programmes a year – and an obvious potential springboard to becoming director general.

Following the departure of deputy director general Mark Byford, whoever becomes the Vision director, along with BBC chief operating officer Caroline Thomson, is also likely to deputise for Thompson.

Just one person so far has admitted they are applying – the acting Vision director George Entwistle. One source said Thompson has picked him out as a future director general, although another said: "He could be the next director general but one."

Independent producer

Former Channel 4 chief executive Michael Jackson is said to be "intrigued" by the Vision job and has had discussions about it. He knows the BBC well, having been both BBC1 and BBC2 controller in the 1990s and responsible for such shows as This Life. Jackson began his television career as an independent producer, so he understands that market.

But he also has experience of the international programming business after he left C4 in 2001 to become president and chief executive of USA Entertainment and then chairman of Universal Television Group. And he has digital knowledge. He has been a senior adviser to internet giant IAC, which owns businesses such as the portal excite.com and ask.com.

Over the last couple of years his name has re-emerged in the UK. He is on the board of Jane Root's production company Nutopia and is a non-executive director of STV. The BBC's director of news Helen Boaden has been touted as an internal rival to Entwistle. She has kept a low profile, probably one of the lowest of any BBC News boss. With her background in radio, news and current affairs her supporters say she realises that if she wants to be director general she needs more populist programming and the "shiny floor experience" that the Vision post would bring - but she dislikes exposure so much it is not obvious she would enjoy the public pressures of the top job.

BBC North

Meanwhile, another BBC name being linked with the Vision role is BBC North boss and ex-BBC1 controller Peter Salmon, although it is understood he has not applied.

Outside the corporation other candidates are said to include another former BBC1 controller, Lorraine Heggessey. After she left the BBC she spent five years as chief executive of Talkback Thames before departing last summer.

According to one well-placed source, Sky's head of entertainment, broadcast operations and news Sophie Turner-Laing - who is also a former BBC executive - is on the long list drawn up by the headhunters for the new Vision director. Whether she would want the role is another matter. When asked by the Guardian in an interview last year if she might return to the BBC one day, she said: "I'm a commercial broadcaster. I'm not sure they'd have anybody from Sky for a very long time."

While the Vision route is one way to climb the ladder to the top job, another could be to follow in Thompson's footsteps and approach it via Channel 4. Some sources say that could put C4's new chief executive David Abraham or his chief creative officer Jay Hunt in line.

They may choose to play down any BBC ambitions (Abraham has certainly done so in private) but denial now means nothing when the moment comes. After all, just a few weeks after he insisted he would stay as chief executive of C4, Thompson said he had changed his mind and moved to become BBC director general after listening to "what Sonia Gandhi called my inner voice".

International candidates have been runners-up for the director general job before but none have so far succeeded, despite the BBC's ambitions for a leader with global experience. There is also speculation that the corporation could make history by appointing its first female DG next time round, giving hope to admirers of the former Channel 5 chief executive Dawn Airey, Turner-Laing and Boaden.

However, the BBC is a unique institution thatrequires some prior experience. One executive said: "Whatever happens, what you have to remember is the director general of the BBC is a very British role. And it has to be someone who has experience of the BBC."

The DG is appointed by the BBC Trust so the fact that there is a new chairman-designate, Lord Patten, has further fuelled speculation about who might one day succeed Thompson. "You've got a new chairman and chairmen like appointing director-generals," says Dyke.

BBC sources say a new Vision director should be appointed by the end of the month or early April. Thompson has the final say on who it will be – he may not appreciate too overt a statement of personal ambition from the shortlisted candidates. With that in mind, perhaps those with their eyes on the top prize should heed the words of Matthew 5:5: "The meek ... shall inherit the earth."